I've seen some of the artwork and photos and read some of the chapters in Dan's upcoming book. It will be an absolute must-have for anyone with even the slightest interest in this genus. Although it is written for the scientific community, Dan has written it in a way approachable by anyone. You'll definitely want to snatch up a copy as soon as it becomes available. I don’t know what the name will be.
As far as Bogert & Del Campo, I would recommend it highly, but remember that this monograph is a half a century old--as Steve said, some of the information is certainly outdated. If only from an historical perspective it deserves a place on any Gila enthusiast’s shelf. It does contain keys, maps etc. of the Heloderma as they were classified in the 50’s (not too much different from how they are today). Very little was known of reproduction in Heloderma back then.
Mark